Well cleaning method using foam containing abrasives

ABSTRACT

A method of cleaning a well liner by contacting the well liner with a gas-liquid foam having entrained therein a quantity of abrasive particles so as to remove scale and other undesirable material from such liner.

[56] References Cited UNITED STATES PATENTS 2,669,809 2/1954McGrath..................... 3,082,073

Bakersfield; John C. McKlnnell, Taft, both of, Calll. [21] Appl. No.838,083

United States Patent [72] Inventors StanleyOJlotchlnon 134/7UX 134/7UX175/69 175/69 166/309X 134/7 175/69X 166/3 12X 3/1963 McAnneny 3,111,17811/1963 Marsh eta1....... 3,130,798 4/1964 Schramm et a1. 3,155,17811/1964 Kirkpatrick 3,272,650 9/1966 MacVittie 3,273,643 9/1966 Billingset a1. 3,463,231 8/1969 l-lutchison et Primary Examiner-Stephen J.-Novosad [22] Filed July 1, I969 [45] Patented June 8, 1971 [73]Assignee Chevron Research Company San Francisco, Calif.

g a well liner by contacting in having entrained therein a as to removescale and other undesirable material from such liner.

GAS SOURCE SOLUTION SOURCE F. E. Johnston, R. L. Freeland, Jr. and

SAND SOURCE Attorneys-A. L. Snow E. J. Keeling ABSTRACT: A method ofcleanin the well liner with a gas-liquid foa quantity of abrasiveparticles so [54] WELL CLEANING METHOD USING FOAM CONTAINING ABRASIVES 6Clalms, 3 Drawing Figs. [52] US.

[51] int. [50] Field of 312, 309; 175/69, 71; 134/7, 8, 22-24; 51/317,

WELL CLEANING METHOD USING FOAM CONTAINING ABRASIVES CROSS REFERENCE TORELATED APPLICATIONS The present invention is related to the field ofinventions disclosed and claimed in copending US. applications Ser. No.704,832, filed Feb. I2, 1968; Ser. No. 720,977, filed Apr. 12, l968 andSer. No. 807,766, filed Mar. 13, 1969.

BACKGROUND OF THE INVENTION This invention relates to a method ofutilizing abrasive particles entrained in foam for cleaning an oil wellliner or the like and, more particularly, this invention provides forcontacting a well liner including the slots thereof with a foam havingentrained therein a plurality of small angular particles at a velocitysufficient to abrade scale and other undesirable material from such awell liner.

As is known in the art, oil is produced from underground formationspenetrated by a well. A well liner is usually placed adjacent aproducing formation and oil is produced through slots or perforations inthe well liner. Such liners are almost always used when the oil-bearingformation tends to be unconsolidated. The well liner holds back theunconsolidated material and allows oil to be produced through the slotsor perforations. As time goes by and such production occurs, however,the well liner often becomes plugged by organic and inorganic materialsuch as asphaltene deposits and scale. As plugging occurs, the amount ofoil which can enter the well through the liner for production therefromis drastically reduced. Many methods have been used heretofore toalleviate this problem. Thus many mechanical scratching devices havebeen used to scratch or scrape off the scale and other deposits. Inaddition, many washing techniques using solvents have also been used toattempt to clean up a well liner. For a number of reasons, none of thesemethods have been entirely satisfactory.

SUMMARY OF THE INVENTION The present invention is directed to providinga method for cleaning well liners utilizing a foam circulating materialhaving abrasive particles entrained therein. The liner is contacted bythe particle-containing foam at a velocity sufficient to abrade andremove undesirable material from such liner and to open the slots orperforations in it. After contacting the liner with such particles, theparticles and any scale or other material are circulated from the welland the well is ready for additional production through the cleanedliner.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides amethod for removing undesirable material such as scale or asphaltenedeposits from a well liner by forming a foam having entrained therein aquantity of abrasive particles and injecting such foam containing theparticles down a well and contacting a well liner with the foam andparticles at a velocity sufficient to remove the undesirable materialsfrom the well liner. in accordance with the invention, a liquid-gas foamis formed by contacting a suitable liquid, such as an aqueous surfactantsolution, with a gas, such as air, to form a foam suitable for use in awell. Abrasive particles are added to the foam and the foam having theparticles entrained therein is injected by suitable means, such as atubing string, down a well to a position adjacent a well liner locatedtherein. The foam is then directed against the well liner and theparticles contained in the foam assist in abrading undesirable materialsfrom the liner to open the slots or perforations of the liner. Suchundesirable material and used particles are circulated up the wellannulus by additional foam which is injected down the tubing andcirculated up the well annulus. When the foam having the particlesentrained therein has cleaned the liner to a desired degree, the foam iscirculated out of the well and the well is ready for additionalproduction.

OBJECTS OF THE INVENTION A particular object of the present invention isto provide for cleaning a well liner by contacting such liner with foamhaving abrasive particles contained therein at a velocity sufficient toabrade and remove undesirable material from such liner and from thewell. Further objects and advantages of the present invention willbecome apparent from the following detailed description read in light ofthe accompanying drawing which is made a part of this specification.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view of the preferredembodiment of apparatus assembled in accordance with the invention foruse in circulating an abrasive foam through a tubing string to a wellliner located in a well, FIG. 2 is a view of an alternative embodimentof apparatus for directing foam from a tubing string to a well liner,and FIG. 3 is a view of another alternative embodiment of apparatus fordirecting foam through the slots of a well liner.

DESCRIPTION OF THE PREFERRED EMBODIMENT Refer now to the drawing and to'FIG. 1 in particular where the preferred embodiment of apparatusassembled in accordance with the present invention is illustrated. FIG.1 shows an elevation view, partially in section, of a well penetratingan oil-producing formation 10. The portion of the well adjacent theproducing formation 10 contains a perforated or otherwise suitablyslotted well liner 12. The well liner 12 is connected by suitable meansto a string or casing 14 which extends from the upper portion of theproducing formation through the earth to the surface. The well liner isplaced during completion of the well and oil from the producingformation l0 enters the well throughthe slots in well liner 12. The oilis moved to the surface by suitable means such as an oil well pump.After many years of such production, the well liner tends to accumulatescale and other undesirable deposits, and often the slots orperforations of the liner become partially or completely plugged. Thisresults in drastically reducing the amount of oil which can enter thewell through the liner. When such plugging occurs, the method of thepresent invention may be utilized to assist in cleaning the liner sothat additional production may be obtained from the well.

In accordance with the preferred embodiment of the invention, a tubingstring 24 is positioned in the well through a suitable wellhead 28. Theparticular size and type of tubing string will depend on the particularwell being serviced. Both segmented tubing strings and continuous tubingstrings are suitable for use in the present invention When using asegmented tubing string, slips 31 are positioned on a slip base plate 30which is connected to the top of the wellhead 28. The slips 31 are usedto hold the tubing string during make up of the string. Stripper rubber35 is used in the wellhead 28 to prevent leakage of foam past the tubingstring where it enters the wellhead. The lower end of the tubing string24 is positioned adjacent the well liner 12 which is to be cleaned. Thetubing string 24 and the well liner l2well casing 14 form a well annulus23. Thus a path for circulating foam through the well is provided in theinterior or tubing string 24 and well annulus 23. A blooie line 41 isconnected through valve 43 and connection 45 to the well annulus 23 forexhausting foam therefrom. The tubing string may be raised or lowered inthe well during foam circulation by hoist means which include atraveling block 58 which is moved by suitable cable 60. A conventionalhoist means or derrick, not shown, is used to move the traveling blockup and down. The elbow joint 46 which is connected to the upper end ofthe tubing string 24 is held in an elevator 62 which is connected bysuitable links 64 to the traveling block 58. Thus when the travelingblock 58 moves up or down the tubing string and the apparatus connectedthereto are also raised or lowered.

Foam is formed by mixing together a surfactant solution and a gas. Thefoam must be a relatively stable foam capable of holding the abrasiveparticles. Thus a suitable foamable solution source 70 and a gas source,such as an air compressor 7I, are located on the surface. Suitablepiping extends from these sources to a common conduit. This conduit 49is connected to both the tubing string 24 and the well annulus 23. Theconduit is connected to the tubing string 24 through flexible conduit48, hammer connection 54, conduit 50 and elbow joint 46. Valve 52 isused to control flow to the tubing string. The conduit 49 is connectedto the well annulus 23 by means of conduit SI and connection 55 viawellhead 28. Valve 53 controls fiow to the well annulus. Thus foam maybe circulated in a normal manner, i.e., down the tubing and up theannulus, or foam circulation may be reversed, i.e., down the annulus andup the tubing. Operating conditions may occasionally dictate that theabrasive foam be reciprocated up and down past the liner to obtain bestresults. This is accomplished by reversing foam injection sequentiallyfrom tubing to liner.

An abrasive material, such as sand, is provided from sand source 72. Thesand is preferably added to the foam after it has been formed throughline 73. Alternatively, the sand may be added to the liquid prior toforming the foam by alternative sand line 74. The preferred abrasivematerial is sand. However, other particulate abrasive material such asangular steel shot may be used. The material should be of the type usedin sand blasting operations to obtain maximum descaling results. Thesize of the particles may vary. However, sizes in excess of one-eighthinch are not normally used.

The foam is formed by bringing a foamable mixture ofa surfactantsolution and gas together. The preferred foam is an aqueous-air foam.Water and a detergent and if desired suitable stabilizing agents aremixed to produce a foamable mixture. Suitable foam and the specificsurfactants which go into the foamable mixtures that make them aredescribed in detail in the above-noted application Ser. No. 704,832,filed Feb. I2, 1968 and now US. Pat. No. 3,463,23l. The disclosure ofsuch application is incorporated herein by reference. A preferred foamfor use in the present invention is a C,,C alkylbenzene sulfonate (ABS)preferably the ammonium salt. The ABS should be added to water to foam afoamable solution in an amount of between 0.5 to 1.0 parts by weight per100 parts water. The foamable solution is mixed with air in a gas toliquid volume ratio of between 3 to 50 SCF to 1 gallon. Superior resultsare obtained when the foam is carrying abrasive particles when thegas/liquid volume ratio is between 10 to SCF to 1 gallon.

As noted above, the abrasive material which in the preferred embodimentis sand, is preferably added to the foam after it has been formedthrough line 73. Suitable means for introducing the sand into the foamconduit are well known in the art. A screw extruder for introducing theparticulate material into the pressurized foam conduit is one suchsuitable means. If it is desired to add the sand to the foamablesolution prior to forming the foam, the sand may be carried in a liquidslurry and injected into the solution line using a pressure vessel suchas is used in sand and gravel packing. Although partieular localconditions of a well may dictate otherwise, it is usually preferred toentrain in the foam between one-half to 6 pounds of sand per gallon offoam solution. A range 2 to 4 pounds of sand per gallon of foam solutionis most preferred.

In the preferred form of the invention, the foam having the abradingsand entrained therein is injected down the well through tubing string24. Thus valve 52 on line 50 is opened to admit foam to the tubing andvalve 53 on line 51 is closed to prevent foam from entering the wellannulus. Valve 43 on most applications a velocity of at east 25 feet perminute is required to provide a minimum abrasive action. It is highlypreferred to circulate the foam at a velocity of at least 300 feet perminute to obtain improved results. The sand and the scale which isremoved from the well liner and the slots thereof are circulated up thewell annulus 23 and dumped at the surface through blooie line 41.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS FIG. 2 shows an alternative formof directing the abrasive foam against the well liner. Thus a smallopening 75 is formed in the lower end of a tubing string 76 and the foamcontaining the abrasive sand particles is directed through one or moresuch openings against the well liner at substantially right anglesthereto to abrade and clean it. The foam and any material removed fromthe liner 77 are circulated up the well annulus as described above.

In FIG. 3 another alternative embodiment of apparatus for use in themethod of the invention is shown. In this embodiment wash cups 82 and 83are utilized to isolate one or more perforations in a liner from therest of the well annulus. Foam is then injected into this isolatedportion of the annulus through a suitable opening 84 in the tubingstring 80. The wash cups 82 and 83 cause the foam to be forced throughthe perforations in the liner 79 adjacent thereto and to move behind theliner and back into the well annulus through the slots above theuppermost wash cup 82. This has the effect of cleaning and abrading theslots or perforations and provides a beneficial cleaning action. It isevident that the method of the present invention may be utilized incombination with other types of washing devices and scratching devices.Such use is, of course, within the scope of the invention.

While preferred embodiments of the invention have been shown anddescribed, it is evident that modifications thereof can be made by oneskilled in the art without departing from the scope of the invention.

lclaim:

l. A method of cleaning a well liner comprising the steps of forming afoam having entrained therein a quantity of abrasive particles,injecting said foam containing said particles down a well and contactinga well liner with said foam and said particles at a velocity sufficientto abrade scale and other undesirable materials from said well liner.

2. A method of claim 1 further characterized in that the abradingparticles are sand having a diameter of less than oneeighth of an inch.

3. The method of claim 1 further characterized in that the foamcontaining said particles is circulated past said well liner at avelocity of at least 25 feet per minute.

41. The method of claim I further characterized in that at least aportion of the foam containing said particles is jetted against theliner at substantially right angles.

5. The method of claim I further characterized in that at least aportion of said foam is directed through slots of the liner.

6. A method according to claim 1 wherein from one-half to 6 pounds ofsand per gallon of foam solution is added to said foam.

2. A method of claim 1 further characterized in that the abradingparticles are sand having a diameter of less than one-eighth of an inch.3. The method of claim 1 fUrther characterized in that the foamcontaining said particles is circulated past said well liner at avelocity of at least 25 feet per minute.
 4. The method of claim 1further characterized in that at least a portion of the foam containingsaid particles is jetted against the liner at substantially rightangles.
 5. The method of claim 1 further characterized in that at leasta portion of said foam is directed through slots of the liner.
 6. Amethod according to claim 1 wherein from one-half to 6 pounds of sandper gallon of foam solution is added to said foam.